While the teachings of the present invention may be applicable to other similar type pneumatic fastener driving tools, it is particularly directed to and will be described in terms of its application to a pneumatic fastener driving tool of the type illustrated in U.S. Pat. No. 4,669,648. The structure and mode of operation of this fastener driving tool will be described in detail hereinafter.
In general, the fastener driving tool of the type to which the present invention is directed is characterized by a cylinder containing a piston/driver assembly. Actuation of the piston/driver assembly is controlled by a main valve at the upper end of the cylinder. The main valve, itself, is controlled by a remote valve. Thus, when the remote valve is shifted from its normal to its actuated position, the main valve will shift from its closed to its open position, allowing air under pressure to enter the cylinder and actuate the piston/driver assembly to drive a fastener into a workpiece.
The remote valve, itself, is controlled by the combination of a trigger actuated valve and a safety actuated valve. The trigger actuated valve is operated by a manual trigger. The safety actuated valve is operated by a workpiece responsive trip or safety, as is known in the art.
The pneumatic fastener driving tool to which the present invention is directed is characterized by the fact that both the trigger actuated valve and the safety actuated valve are of the on-off type and both must be opened in order to shift the remote valve from its normal to its actuated position. However, it makes no difference which of the safety actuated valve and trigger actuated valve is opened first, so long as both of them are opened.
A problem arises from the fact that various safety codes require that pneumatic fastener driving tools have restrictive triggers, such that the workpiece responsive safety must be operated before the manual trigger. The present invention teaches trigger actuated valve/safety actuated valve arrangements which render the manual trigger of the tool a restrictive trigger, which operates the tool only if the workpiece responsive safety has been operated before the manual trigger. The invention is based upon the discovery that a fastener driving tool of the type to which the present invention is directed can be provided as a restrictive trigger tool, upon modification of the trigger actuated valve and replacement of the prior art safety actuated on-off valve with a safety actuated pressure controlled valve of the present invention. Alternatively, a restrictive trigger tool can be achieved with the original safety actuated on-off valve and replacement of the on-off trigger actuated valve with a pressure controlled trigger actuated valve. According to the present invention, such pneumatic fastener driving tools can be manufactured as restrictive trigger tools, and existing tools can be easily modified to have the restrictive trigger mode of operation.